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Date:   Thu, 6 Apr 2023 18:04:18 +0200
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Subject: Re: [PATCH 2/2] ARM: dts: imx6ull-dhcor: Add Marantec maveo box
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To:     Christoph Niedermaier <cniedermaier@dh-electronics.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Shawn Guo <shawnguo@kernel.org>, Li Yang <leoyang.li@nxp.com>,
        Fabio Estevam <festevam@denx.de>,
        NXP Linux Team <linux-imx@nxp.com>,
        kernel <kernel@dh-electronics.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>
References: <20230405160258.46998-1-cniedermaier@dh-electronics.com>
 <20230405160258.46998-2-cniedermaier@dh-electronics.com>
 <05fa147c-116b-59b4-d14b-760bbefd7602@denx.de>
 <e7aa3b3220e148ee96f5a1c361721845@dh-electronics.com>
 <42737c19-698f-8cc8-45b2-8ff08a274f87@denx.de>
 <531df359744f4bdb9fd34eafc864d2bc@dh-electronics.com>
 <50c88cc4-e046-6c43-2d35-116d1d4ea2f8@denx.de>
 <622e846f1d2c4f8abba171202640d1d3@dh-electronics.com>
From:   Marek Vasut <marex@denx.de>
In-Reply-To: <622e846f1d2c4f8abba171202640d1d3@dh-electronics.com>
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On 4/6/23 17:44, Christoph Niedermaier wrote:
> From: Marek Vasut [mailto:marex@denx.de]
> Sent: Thursday, April 6, 2023 4:10 PM
>> On 4/6/23 10:37, Christoph Niedermaier wrote:
>>> From: Marek Vasut [mailto:marex@denx.de]
>>> Sent: Wednesday, April 5, 2023 8:47 PM
>>>> On 4/5/23 20:24, Christoph Niedermaier wrote:
>>>>> From: Marek Vasut [mailto:marex@denx.de]
>>>>> Sent: Wednesday, April 5, 2023 6:25 PM
>>>>>> On 4/5/23 18:02, Christoph Niedermaier wrote:
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> +/ {
>>>>>>> +     model = "DH electronics i.MX6ULL DHCOR on maveo box";
>>>>>>> +     compatible = "dh,imx6ull-dhcor-maveo-box", "dh,imx6ull-dhcor-som",
>>>>>>> +                  "fsl,imx6ull";
>>>>>>> +
>>>>>>> +     aliases {
>>>>>>> +             /delete-property/ mmc0; /* Avoid double definitions */
>>>>>>> +             /delete-property/ mmc1;
>>>>>>> +             mmc2 = &usdhc2; /* eMMC should be mmc2 */
>>>>>>
>>>>>> Why not mmc0 ?
>>>>>>
>>>>>> Use root=PARTUUID= when booting to avoid any dependency on
>>>>>> root=/dev/mmcblk2pN enumeration.
>>>>>
>>>>> This is due to software interchangeability with the DHCOM
>>>>> i.MX6ULL, where the eMMC is always mmc2.
>>>>
>>>> +CC Ulf , I vaguely recall some discussion about this enumeration and I
>>>> am not sure one can really depend on that.
>>>
>>> That why I think it good to have a defined number for mmcblk devices
>>> on an embedded system. An excerpt from [1]:
>>
>> I might be misremembering this, but could it be that, if any non-OF
>> SDMMC controller probes early and hogs the /dev/mmcblk2 before the OF
>> ones have a chance to probe, then the OF ones would fail to probe ?
>>
>>> Alternative solutions like PARTUUIDs do not cover the case where multiple
>>> mmcblk devices contain the same image.
>>
>> I agree, this is indeed a downside of PARTUUID .
>>
>>> This is a common issue on devices
>>> that can boot both from eMMC (for regular boot) and SD cards (as a
>>> temporary boot medium for development). When a firmware image is
>>> installed to eMMC after a test boot via SD card, there will be no
>>> reliable way to refer to a specific device using (PART)UUIDs oder
>>> LABELs
>>
>> This can be solved by the installer updating the PARTUUID on the eMMC
>> however.
>>
>>> [1] https://patchwork.kernel.org/project/linux-mmc/patch/20200825134441.17537-2-matthias.schiffer@ew.tq-group.com/
>>>
>>> So far I have never had a problem with numbering mmcblk devices via aliases.
>>
>> Based on the above, I don't think either the aliases or PARTUUID is a
>> perfect solution, but the aliases should be fine for mx6ull at least?
>> So I think we can conclude this discussion thread ?
> 
> Yes, I will send a new version with the changes on the first patch.

Thank you